1994 рік

Analytical-grade piperazine was dissolved in methanol and reacted with commercial-grade poly(vinyl chloride) powders over a range of temperatures from 25 to 64°C and times from 0.17 to 49 days. The products were aminated polymers that also contained conjugated double bonds. Chemical analysis of the resulting powders showed that up to 1.6 wt% N was possible in this solid-liquid heterogeneous reaction, although insolubility of the aminated polymer in tetrahydrofuran was always realized by 0.8 wt % N content. In those polymer formulations that were soluble, membranes were cast from solution using o-nitrophenyloctyl ether and potassium tetrakis(p-chiorophenyl)borate as the plasticizer and negatively charged sites, respectively. After conditioning, many of these fixed-site proton carrier membranes showed Nernstian pH sensitivity in potentiometric cells, independent of synthesis parameters. The nitrogen content of the aminated PVC and the pH sensitivity of the membrane correlated below a limiting nitrogen content, where Nernstian behaviour was generally observed over a range from 0.4 to 0.8 wt% N content. A three-dimensional plot over the soluble region of the polymer predicted the overall dependence of the reaction parameters, from which an activation energy (17 kcal mol- 1) was determined for the substitution process. A time-temperature correspondence was demonstrated that allowed the construction of a master curve of amination in which the shift factor was of the same form as either the Williams-Landel-Ferry equation or a rearranged Doolittle equation. This format was extended to three dimensions, where the pH sensitivity is shown as a function of both the weight percentage N content and the shift factor

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Imide-aryl ether thiophene copolymers were prepared and their thermal and mechanical properties were investigated. A key feature of these copolymers is the incorporation of the 2,5-thiophene moiety using 5,5'-bis[(3-aminophenoxy)thienyl-2] ketone or 5,5'-bis[(4-aminophenoxy)thienyl-2] ketone as diamines in polyimide syntheses. The preparation of these thiophene diamines involved the nucleophilic aromatic substitution of bis(5-chlorothienyl-2) ketone with either 3- or 4-aminophenol in N-methyl-2-pyrrolidinone using potassium carbonate. These diamines were reacted with various compositions of pyromellitic dianhydride and 4,4'-oxydianiline to synthesize the desired poly(amic acid)s. Films were cast and cured (300°C) to effect the imide formation, and the resulting films showed tough ductile mechanical properties with high glass transition temperatures that decreased with increasing thiophene diamine content.

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The effects of thickening agent, magnesium oxide (MgO), on the curing behaviour of unsaturated polyester (UP) resins at ll0°C were investigated by an approach of integrated reaction kinetics, rheology and morphology measurements using d.s.c., Fourier transform i.r. (FTi.r.) spectroscopy, a Haake viscometer, and SEM. For the UP resins thickened with 4% MgO at room temperature for 192 h, isothermal d.s.c. rate profiles at 110°C showed that the induction time, t~, and the time to reach the maximum rate, tin, were prolonged and the final overall C=C conversion was reduced when compared with those for the neat UP resins. For the thickened UP resins, FTi.r. measurements revealed that the conversion of styrene was always higher than that of polyester C=C bonds throughout the reaction. Rheokinetic data showed higher gelation time and gel conversion of total C~---C bonds than for the neat UP resins. Also, SEM micrographs showed that the fractured surface after the cure appeared less smooth. Finally, all the experimental results have been elucidated in light of the formation of thickening-induced microdomains of aggregates for polyester chain segments prior to cure, as observed by SEM micrographs, and the associated reduction of reactivity for styrene and, especially, polyester C=C bonds in these microdomains during the cure

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Studies on the crystallization of polymers are usually carried out by dilatometry, differential scanning calorimetry (d.s.c.) and optical microscopy. These methods have been widely used in the analysis of crystallization kinetics using the Avrami equation. Direct determination of nucleation rate and density is only possible by the optical microscope technique. We have employed a new technique for studying the crystallization behaviour of polymers by using a dynamic mechanical method. This method is capable of detecting the onset of nucleation. Semiquantitative data on the nucleation density and the initial crystallization rate may also be deduced by this method. Results from the dynamic mechanical method are cross-compared with d.s.c, and optical microscope data for polypropylene, polyethylene and their blends, and are shown to be mutually consistent.

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In aqueous solutions many polymers may be gelled by adding an appropriate cross-linking agent, and the system that is obtained is usually characterized by using rheological measurements. Among the most investigated properties of such systems is their gelation kinetics. In this work we deal with a system where the polymer is a nonionic polyacrylamide and the cross-linking agent is glyoxal. We focus our study in particular on the gelation kinetics by following the change in elastic modulus under given experimental conditions. In an alkaline medium and at low temperatures, the bond formation rate is found to follow certain power laws with relation to both polymer and glyoxal concentration. However, at an alkaline pH and at sufficiently high temperatures, the system loses its gelled structure due to a 'parasitic' chemical reaction. This reaction may be eliminated by reducing the pH to an acid value, but at the same time the gelation kinetics become modified as the complexation process is then different from the alkaline case.

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The morphology of AB and BAB block copolymers consisting of one amorphous block (A) and liquid crystalline blocks (B) has been investigated using TEM, low angle electron diffraction and small angle X-ray diffraction. All samples of poly[styrene-block-2-(3-cholsteryl-oxycarbonyloxy)ethyl methacrylate] (PS-PChEMA) with a volume fraction OPS between 0.3 and 0.4 show a morphology consisting of PS rods in a PChEMA matrix. The rods are organized in a tetragonal lattice rather than the expected hexagonal structure.

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The sol-gel-glass transformations were examined in the thermosets of diglycidyi ether of bisphenol A (DGEBA) and diglycidylaniline (DGA) cured with 4,4'-diaminodiphenylmethane (DDM) at 70°C by using time-resolved fluorescence, Fourier-transform (FT) Raman spectroscopy, an ultrasonic technique and torque measurements. The rotational correlation times of substituted styryl and cyanine dyes showing a twisted intramolecular charge-transfer increase as the isothermal cure reaction proceeds and are sensitive to gelation. The chromophores detect the local viscosity of the surroundings. In the case of DGEBA/DDM, the extent of the epoxide ring reaction, obtained from FT-Raman studies over the whole curing process, was used to determine the variation of the glass transition temperature and the reduced free volume during crosslinking. Thus, it was possible to relate quantitatively the increase of the rotational correlation time of the dyes to the decrease of the reduced free volume. The variation of the ultrasonic velocity and absorption in the course of curing indicates vitrification (dynamic glass transition), but shows no characteristics with respect to gelation. Differences in the curing behaviour of DGEBA/DDM and DGA/DDM were clearly evident.

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The thermally stimulated depolarization current technique has been used to study the relaxation behaviour in solvent-cast blends of poly(vinyl chloride) (PVC) and acrylonitrile-butadiene-styrene (ABS). The effects of the forming conditions (field, temperature and time) on depolarization have been investigated. The data on blends with components in various weight ratios indicate that the blends are not compatible enough to show one relaxation peak and the 40:60 PVC/ABS blend shows the greatest depolarization current. The blends show two relaxation processes corresponding respectively to the glass transitions of PVC and ABS. Partial polarization and peak-cleaning techniques have been used to obtain both c? peaks as a function of blend composition. Curve fitting was carried out and the activation energy Ea and the pre-exponential factor Zo were calculated. The data have been used for investigations of relaxations that obey an Arrhenius-like law. Analysis of the data shows that it is possible to study the relaxation behaviour in this system, which was found to be controlled by the free-volume mechanism described by the Williams- Landel-Ferry equation.

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Permselective separation between water and water-soluble organics was investigated up to high concentration levels through crosslinked and metal complexed membranes of hybrid Schiff-base derivatives of poly(allylamine), which were prepared by the reaction between pyridine-2-carboxaldehyde (P) and salicyl aldehyde (S) with varying ratios of P/S. The complexed membranes had strong hydrophilic character and showed an increased flux and high permselective separation for t-butanol and tetrahydrofuran at high concentrations. Correlations between the performance of the complexed membranes and the physicochemical parameters, especially the solubility parameters, of alcohols and aprotic solutes were studied and discussed. It was found that a membrane with a higher P/S value tended to reject the aprotic solute with a smaller solubility parameter, while other physical properties of the alcohols also effected the alcohol separation

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Polycarbonate obtained by solid state polycondensation (SSP) crystallizes in an orthorhombic configuration with a= 12.1 A, b= 10.1 A and c=22.0A. Its morphology is of non-spherulitic lamellar type, while that of melt or solution crystallized commercial polycarbonate is distinctly spherulitic. These changes in crystalline structure and morphology can be explained, in the present case, on the basis of restricted mobility of the chains and the crystal growth in an extended chain configuration during the SSP step.

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